5.7.513: Your IP is on the recipient’s own block list
Microsoft 365 returns 5.7.513 when the recipient’s organization has added your sending IP to its own custom block list (AS16012607). This is the recipient’s decision, not Microsoft’s, so the delist portal will not help. Only the recipient organization can remove the block.
The exact message
Microsoft 365 / Exchange Online
5.7.513 Service unavailable, Client host [$ConnectingIP] blocked by $recipientDomain using Customer Block list (AS16012607)
Why it happens
- The recipient’s admin blocked your IP, often after unwanted mail.
How to fix it
- Stop emailing that organization.
- If the block is a mistake, contact the recipient through another channel and ask them to remove it.
If you send cold email
A customer block list entry is a clear signal that the organization does not want your mail. Suppress the whole domain in your outreach tool.
How WarmHawk handles it
WarmHawk pauses a mailbox on its own once its hard-bounce rate passes 5% over at least 20 sends, and pauses a campaign at that campaign’s own bounce threshold, so a bad list stops before it drags the domain down. Every sending domain is re-checked against DNS blocklists hourly, and a mailbox only reaches campaign volume after at least 14 days of warmup with a 90% inbox rate. A mailbox whose inbox rate falls below 70% goes back to warmup. How WarmHawk works →
Check your domain now
These free checkers read your live DNS: no account, up to 15 domains at once.
Related bounce codes
- 5.7.606Access denied, banned sending IP
- 5.7.12Recipient only accepts mail from inside its organization
Sources, checked 2026-09-29: Microsoft Learn: NDRs and SMTP errors in Exchange Online. Have a different bounce? Paste it into the decoder →
Questions
5.7.513 questions
What does 5.7.513 mean?+
Microsoft 365 returns 5.7.513 when the recipient’s organization has added your sending IP to its own custom block list (AS16012607). This is the recipient’s decision, not Microsoft’s, so the delist portal will not help. Only the recipient organization can remove the block.
Is 5.7.513 a temporary or permanent error?+
Permanent. The message will not be retried, and sending it again unchanged will fail the same way until the cause is fixed.
How do I fix 5.7.513?+
Stop emailing that organization. If the block is a mistake, contact the recipient through another channel and ask them to remove it.